A standard bending machine has a housing, a holder on the housing for retaining the workpiece with its axis nondisplaceable and normally horizontal relative to the housing and for advancing the workpiece in a feed direction parallel to the axis, and a mandrel formed with an arcuate groove centered on an axis transverse to the longitudinal axis and spaced transversely therefrom. This mandrel carries an inner jaw forming a continuation of the groove and rotatable with the mandrel about the mandrel axis. An arm pivotal on the housing about the mandrel axis carries an outer jaw generally complementary to the inner jaw. A guide mainly upstream of the mandrel has a guide groove confronting the groove of the mandrel and centered on the longitudinal workpiece axis. The workpiece held in the holding means fits in the grooves of the guide and mandrel simultaneously. An actuator pivots the support about the mandrel axis to bend the workpiece between the jaws and the guide.
Thus with this system the two jaws grip the workpiece and then the mandrel pivots with both the jaws. This bends the workpiece through an angle determined by the amount the jaws and mandrel pivot and gives the bend thus formed a curvature corresponding to that of the mandrel. The bending operation typically advances the workpiece slightly longitudinally, and the guide prevents any bending of the workpiece downstream of the mandrel.
In this type of arrangement the guide, mandrel, and inner jaw are mounted on a common transversely displaceable support. Thus when the transverse dimension of the workpiece change it is necessary to change the mandrel and both jaws for the new workpiece, and then to appropriately reposition the guide which must be moved on the subassembly. Obviously this is a cumbersome and difficult procedure incurring quite some down time between runs.
Another disadvantage of these arrangements is that they only allow multiple nonaligned curves or opposite curves to be formed on circular-section workpieces. Square- or other polygonal-section workpieces cannot be rotated while engaged with the mandrel and guide to form nonaligned bends.